The attraction of primordial germ cells (PGCs) by the gonadal anlage (germinal ridge; GR) in vitro has been demonstrated in the chick. PGCs were isolated from circulating blood of stage 13 embryos (Hamburger and Hamilton, 1951), placed between the GR and other embryonic tissues (neural tube, heart, allantois, liver) as controls separated by a distance of 170 microns on collagen-coated substrate, and cultured with modified medium 199 (Kuwana and Fujimoto, Anat. Rec., 209:337-343, 1984) containing 10% fetal calf serum (pH 7.3). The behavior of PGCs was observed for 3 hr by 16-mm time-lapse microcinematography. PGCs showed directional movement toward GR. Also, there was a stronger attractive effect on the PGCs by GR from stage 13 embryos than by GR from later stage embryos. These results suggest that PGCs are attracted by some factor emitted from GR.